In a typical ducted heating, ventilation, and air conditioning (“HVAC”) system, a single blower in an indoor air handler circulates air to various parts of a building through a system of ducts. In a typical zoned HVAC system, the ducts are divided into several zones, one for each part of a building that is desired to be controlled independently of the other zones. Zoned HVAC systems require a large plenum with smaller duct branches feeding conditioned air from the plenum to the interior space. A set of dampers are field installed into the duct branches, downstream of the supply plenum, with at least one damper for each zone. These dampers can be opened or closed, to direct more or less air to a particular zone as needed to satisfy the desired comfort level in that zone.